Determination of Total Content of Rare Earths in Deep-Sea Sediments by Inductively Coupled Plasma Mass Spectrometry after Microwave Digestion

A method for the determination of total content of rare earths in deep-sea sediments by inductively coupled plasma mass spectrometry (ICP-MS) after microwave digestion was established. The wet samples of deep-sea sediments were dried, crushed and removed impurities, and then dried again after sieving. The sample (0.20 g) was taken and added into the microwave digestion tank, 5.0 mL nitric acid and 2.0 mL hydrofluoric acid were added for microwave digestion under temperature programmed condition. Perchloric acid (3.0 mL) was added to remove acid, and 50% (volume fraction) nitric acid solution was added and heated to dissolve the salt in the sample. After cooling, the solution was diluted by water and its volume was made up to 50 mL. An aliquot of 5.0 mL solution was taken and diluted to 50 mL with 2% (volume fraction) nitric acid solution. 10 μg·L^-1 indium internal standard solution was added online, and the contents of rare earth oxides were determined under the optimized ICP-MS working conditions. The results showed that mass concentrations of 15 rare earth oxides were linearly related with the ratios of the response values of rare earth oxides to indium internal standard element in definite ranges, with the same correlation coefficient of 0.999 9 and detection limits (3s) in the range of 0.006 2-0.060 0 μg·g^-1. Tests for precision, spiked recovery and method comparison were made, giving results of RSDs (n=11) of the determined values in the range of 1.1%-2.9% and recovery in the range of 96.0%-104%, and the determined values were consistent with those obtained by the national standard method GB/T 17417.1-2010.